I'd like to design a single board Linux computer, maybe something ARM-based but I really don't know that much about the hardware side of computers. Does anyone know where I could get some information to get started? Thnx
There are many topics about this, and 99.9% of them say (paraphrased):
"You are not good enough. Unless you have many many years in industrial professional board design for similarly complex embedded systems, start with Arduino and making your own (successfully), and perhaps go get a bachelors in Electronics Engineering and a few years experience at a company that does that sort of thing. THEN you will be successful and have the skills and knowledge to do what you want"
I hope that helps - but do know, it IS possible. Just very hard and you will waste a lot of time and money unless you get the required experience and knowledge first, and honestly for a singleboard computer style architecture similar to the raspberry pi and beaglebones, you really do need all of that under your belt to make it work properly.
Take a look at the OMAP processor from Texas Instruments. There's quite a lot of data available on those, compared to a lot of the ARM chips from other vendors. Nowadays, also the Broadcom processor which is used in Raspberry Pi has at least some public documentation, much because of Raspberry Pi.
The core design for Cortex A is always similar: the ARM has pads on top of the IC for connecting a multi-die memory chip which has two dies (chips) in the same package: A mobile DDR3 DRAM and a Nand Flash to boot from. This design is fixed, so there's no thinking involved for you to do, a good thing in this respect.
In addition to the main memory, you'll need to provide power and clocking. These should be fairly well explained in the datasheets also. Then you'll need some I/O: bring out USB ports, UART for the console and SD card connection.
Study how the chip is supposed to boot (Linux) from http://processors.wiki.ti.com/index.php/Boot_Sequence or the datasheets and application notes for your processor. You should figure out much of the needed stuff by studying the boot sequence. When you power up the device and get anything from the console, you're much closer to success.
These devices are complex, but the complexity is often exaggerated. Take a look for example at the Raspberry Pi schematic at http://www.raspberrypi.org/wp-content/uploads/2012/04/Raspberry-Pi-Schematics-R1.0.pdf. That's rather simple, I would say; there's mainly just the main CPU and a few external connections. Just the Ethernet looks a bit complex. And you don't need to support every feature of the chip at once. Also, even if you're not successful, you have learned a lot in the process.
Finally, add a video output for a more capable display than the serial console. Add a RCA connector for the Video DAC and HDMI if it's supported by the chip. Find linux distributions which are already targetting your chip, such as Angstrom or others; scout the web pages of already existing single board computers such as the Beagleboard for OMAP or the Raspberry Pi for Broadcom.
One more hint: If you're not accustomed to soldering these BGA beasts with hundreds of balls, find a cell phone repair shop. They'll be able to solder the main chip and the memory for you, no problem.
First of all, unless you are willing to spend hundreds of hours and probably a thousand dollars (minimum) on this, it is not a good idea.
Good news, since you won't be selling your board, you can get a hobbyist version of Eagle which is good for up to 6-layer 4" x 6" board for $169.
Bad news, is because of all the surface mount components inclduding BGA, you likely won't be able to assemble your own boards, so each board spin is going to cost perhaps $500 or more -- and I guarantee you're not going to get it right the first time.
Pick an open-source hardware design -- like the BeagleBone Black -- as a starting point. The Raspberry Pi design is closed source, so avoid that.